Magnetocrystalline anisotropy of Laves phase Fe2Ta1-xWx from first principles: Effect of 3d-5d hybridization

Themagnetic properties of Fe2Ta and Fe(2)Win the hexagonal Laves phase are computed using density functional theory in the generalized gradient approximation, with the full potential linearized augmented plane-wave method. The alloy Fe2Ta1-x W-x is studied using the virtual crystal approximation to treat disorder, with some comparisons to supercell calculations. Fe2Ta is found to be ferromagnetic with a saturation magnetization of mu M-0(s) = 0.66 T while, in contrast to earlier computational work, Fe2W is found to be ferrimagnetic with mu M-0(s) = 0.35 T. The transition from the ferri-to the ferromagnetic state occurs for x <= 0.1. The magnetocrystalline anisotropy energy (MAE) is calculated to 1.25 MJ/m(3) for Fe2Ta and 0.87 MJ/m(3) for Fe2W. TheMAE is found to be smaller for all values x in Fe2Ta1-x W-x than for the end compounds and it is negative (in-plane anisotropy) for 0.1 <= x <= 0.9. The MAE is carefully analyzed in terms of the electronic structure. Even though there are weak 5d contributions to the density of states at the Fermi energy in both end compounds, a reciprocal space analysis, using themagnetic force theorem, reveals that the MAE originates mainly from regions of the Brillouin zone with strong 3d-5d hybridization near the Fermi energy. Perturbation theory and its applicability in relation to the MAE is discussed.